1. Field of the Invention
The present invention relates to chromatographic technology, and more particularly to a gradient pump apparatus used for performing chromatography at a flow rate area of nano-liter per minute (10−9 L/min), and a chromatograph using the gradient pump apparatus.
2. Description of the Related Art
Several techniques have hitherto been proposed for chromatographs in which chromatography of a mixture is performed through gradient elution at a flow rate in units of nano-liter per minute.
According to techniques disclosed in a Patent References 1 JP,A 2002-71657 and a Patent Reference 2 JP,A 2002-365272, for example, plural types of gradient solutions required for one analysis item are filled in one or plural flow passages beforehand, and those solutions are successively fed by a pump capable of feeding a solution at a constant flow rate.
Also, a Patent reference 3 JP,A 2003-98166 discloses another technique. According to this technique, at least two feeder units are communicated with each other, and the pressure of a solution fed from a first feeder unit is sensed by a pressure sensor so that the solution is delivered at a desired setting value. Then, a second feeder unit pre-pressurizes the solution corresponding to the delivery pressure of the first feeder unit. In other words, this technique is intended to feed the solution with high accuracy free from disturbances in the solution feed.
According to still another known technique, a gradient solution is fed by a pump capable of feeding the solution at a flow rate in units of micro-liter per minute (10−6 L/min), and a splitter is disposed in a flow passage to split a part of the fed solution such that the solution can be fed at a flow rate in units of nano-liter per minute.
Still another known technique employs a plurality of pumps each utilizing an electroosmotic flow. Then, gradient feed is performed by feeding plural types of solutions with the respective pumps while directly mixing the solutions with each other.